Pharmaceutical developments have yielded dozens of new drugs each year for the past decade. As the identification and understanding of the various hormones, cytokines, neurotransmitters, and various other chemical regulators and messengers has increased, the ability to harness these substances therapeutically also increases. Additionally, with the advent of gene therapy, a new method of treating disease is beginning to be developed.
The significant advances in the therapeutic substances delivered to patients have been accompanied by a somewhat slower development of methods and means of drug delivery. Some of the newer substances are simply not amenable to the paradigm of taking a pill once or a few times a day. For instance, a number of newly developed substances, such as peptides and strands of DNA, are deactivated or destroyed by the gastrointestinal system, immune system, liver, and/or lymphatic system before they reach the systemic circulation in any significant or reproducible level. Other substances must be maintained at a minimum level in order to achieve a therapeutic effect, e.g., heparin. Other substances have a narrow therapeutic window, i.e., the minimum required dose is not far below the maximum recommended dose. Additional examples exist, including substances that may need to be targeted to a site to avoid systemic side effects.
Several methods of convenient parenteral drug administration are now commercially available. Depot formulations of medications have been available for some years, e.g., Depo-Provera, a form of contraception that lasts to 3 months. Transdermal patches are available for the delivery of substances such as fentanyl, nicotine and testosterone. A long-lasting, slow-dissolving formulation of contraceptive is now available from Norplant, and provides a means of contraception that offers protection from pregnancy for up to 5 years.
More invasive systems have become available recently as well. External infusion pumps have been available for a number of years, e.g., the Medtronic MiniMed external insulin pump, made by Medtronic MiniMed Inc. of Northridge, Calif. Implantable infusion pumps are also available for systemic delivery of substances, e.g., the Medtronic MiniMed implantable insulin pump. External and internal infusion pumps are now also used for the delivery of substances to a targeted area, e.g., intrathecal delivery of opiates and cancer site delivery of chemotherapy agents. The infusion rate of some such systems may be adjusted transcutaneously.
The DURECT DUROS osmotic infusion pump, commercially available from Durect, of Cupertino, Calif., is typically implanted via a minimally invasive procedure and provides delivery of medication for up to several months. However, the infusion rate is not adjustable following implantation.
The following U.S. patents describe various types of infusion pumps known in the art: U.S. Pat. Nos. 3,731,681; 4,457,752; 4,557,673; 4,911,616; 5,041,107; 5,045,064; 5,049,141; 5,514,103; 5,637,095; 5,678,296; 5,697,951; 5,733,259; 5,785,681; 5,697,951; 5,733,259; 5,785,681; 5,820,589; 5,888,530; 5,957,890; 6,120,665; 5,667,491; 6,022,316; 6,014,584; 5,869,326; and 6,110,161.